U.S. Vice President Joe Biden delivers a speech Friday at Yonsei University in Seoul, South Korea. (Lee Jin-man / AP)

SEOUL, SOUTH KOREA — Seeking to reassure wary allies, Vice President Joe Biden on Friday pushed back against those who question America's commitment to Asia, which has at times been obscured by an array of distractions at home and abroad.

But Biden warned that without trust and common ground rules, the White House's economic and security goals in Asia could be threatened by mounting tensions in the region.

"This is one of those inflection points in history," Biden said in a speech at an elite South Korean university. "We actually have a chance — a chance — to bend history just slightly."

Biden, nearing the end of a weeklong trip through Asia, outlined a broad vision for a U.S.-Asia bond in which cooperation coexists with intense competition. Tracing the arc of South Korea's evolution since the end of the Korean War, Biden held up this northeast Asian nation as a model for others seeking to emerge from chaos and authoritarianism.

To that end, Biden called on Asian countries to open their economies, drop trade barriers, create opportunities for women and cooperate on environmental protection. He called for Asia to adopt a single set of rules to govern relations between nations in a neighborhood where many of the most powerful nations are bitterly feuding.

"With this growth have come new tensions, above and beyond the enduring threats that we face," Biden said. "The rules and norms that help advance security and prosperity are still evolving to keep pace with the remarkable changes of the 21st century."

Such threats became the backdrop for Biden's stops in South Korea, Japan and China, where the vice president found himself playing mediator for pressing international disputes in a departure from the softer diplomacy typical of vice presidential visits.

South Korea and Japan, the two closest U.S. allies in the region, are engaged in a painful dispute driven by historical enmities dating nearly a century. And there are new, worrying signs from North Korea. Biden vowed the world would not tolerate Pyongyang's nuclear weapons program, adding the U.S. was willing to resume multiparty talks with the North if it agrees to full denuclearization.

In the choppy waters separating South Korea, China and Japan, a turbulent dispute over Beijing's claim to airspace over contested islands hung over Biden's Asia trip. Seizing an opportunity to implore Asian nations to stop provoking one another, Biden said he had stressed to Chinese President Xi Jinping that the U.S. military plans to ignore China's demand that planes flying through the airspace first notify Beijing.

"It will have no effect on American operations. Just ask my general," Biden said. "None. Zero."

The vice president's words, like his trip to Asia, sought to put a fine point on the Obama administration's intention to realign America's foreign-policy focus toward Asia. The U.S. sees the potential for massive growth here but worries that authoritarian China will fill the power void by asserting itself more aggressively against its neighbors.

"If we're going to be honest about it, China is not the only country being assertive right now," Jonathan Pollack, an Asia policy expert at the non-partisan Brookings Institution, said ahead of Biden's speech. "All the states involved are trying to buy themselves more latitude in their decision-making, more space. That's all well and good — until something you don't want to happen, does."

Plans to increase U.S. influence, military presence and diplomatic outreach in Asia have been complicated by Iran, Syria and Egypt, which have commandeered much of the foreign policy bandwidth. In Washington, the abysmal rollout of Obama's health care law and intense gridlock in Congress have kept the White House bogged down in domestic matters.

South Korea's own concerns about frictions in the region were on display earlier Friday when Biden met with President Park Geun-hye at her office amid the sprawling gardens of Seoul's Blue House.

"At a time when we have recently been seeing growing volatility and tensions in northeast Asia, it is very helpful for peace in northeast Asia to have a vice president with such profound insight into foreign affairs travel to this region," she said through a translator.

Before returning to Washington on Saturday, Biden was to lay a wreath at a ceremony honoring fallen U.S. troops. He'll conclude his trip with a visit to the Demilitarized Zone between South Korea and North Korea, a potent symbol of the deep mistrust that continues to estrange South Korea from its northern neighbor.